Field of the Invention
The present invention relates to the formation of reinforced plastic structures and particularly those made by adhering together preformed components or molding a form to one or more preformed components. It is very costly to make molds to form large reinforced plastic components and particularly those having compound curvatures. As an alternative to the costly process of one-part molding, it is possible to fabricate smaller components and thereafter adhere the same together. Another process for joining parts is known as co-molding wherein one or more parts are premolded and another part is directly molded thereto to form an integral structure. In either case, the use of greatly simplified mold shapes is possible by adhering or molding together of smaller components. However, a problem encountered in either co-molding or adhering preformed plastic components together is in providing satisfactory bond strength between the parts being joined since they normally involve very smooth surfaces which makes bonding difficult.
Accordingly, it is common practice to somehow roughen the surfaces being adhered together so that the cementing of adhering material can provide a strong mechanical connection between the parts. In the past this roughening has been achieved by sanding, etching, sand blasting, vapor honing, machining and other such post-molding processes.
The present invention relates to an improvement whereby during the formation or molding of the individual parts, a three-dimensional or rough bonding surface is concurrently provided. To properly understand the invention, it is first necessary to understand a typical reinforced composite material of which such parts may be formed. One such composite material in its simplest form includes an open-cell resilient foam layer which is overlayed with a layer of high strength filaments, such as fiberglass strands, and which foam layer is impregnated with a thermosetting resinous material, such as epoxy or polyester. The impregnated composite is then placed within a mold and compressed so that the resin fills substantially all of the open-cells of the foam layer and the excess resin is extruded therefrom so as to encapsulate the filament layer. Structures made by this type of process are shown in U.S. Pat. No. 3,193,441 Schafer and in copending application Ser. No. 519,496 Dirks, filed Oct. 31, 1974. Parts made by the aforedescribed method result in a resin matrix which extends throughout the composite and which matrix extends to the surfaces of the composite and normally provides a smooth finish. In view of such smooth finish it is difficult to satisfactorily bond together such components without providing an intermediate roughening operation. Applicants have developed a unique method whereby during the process by which such reinforced composite structures are formed, roughened portions are simultaneously provided which enables complementary parts to be bonded together without the necessity of such an intermediate roughing process.